Astrophysical and cosmological observations show that most of the
matter in the Universe is dark and nonbaryonic, whose intrinsic nature is
still unknown [1]}, [2]}, [3]}. Compelling theoretical
models assume that dark matter
consists of weakly interacting massive particles (WIMPs), a simple
hypothesis able to explain the most crucial phenomenology [4]} with relative ease, like rotation curves of
spiral galaxies, the observations of anisotropies of
the cosmic microwave background, gravitational lensing at galactic scale, and the big-bang nucleosynthesis. Present theoretical research
describes the interaction between WIMPs and target nuclei
in terms of effective field theory (EFT) operators
[5]}, [6]}, [7]}. The lowest-order
term in a systematic nonrelativistic expansion is an
interaction that does not depend on
the relative velocity \(v\)  of the incoming particle or on the momentum
transfer \(\vec{q}\) , which can be parametrized by
spin-independent (SI) and spin-dependent cross sections. The SI cross
section is the only one relevant for spin-zero nuclei and, if WIMPs interact
coherently with all nucleons, it is
enhanced by a factor equal to the mass number \(A\) 
relative to incoherent cross sections like the spin-dependent cross section.
